This invention relates generally to low force switches, and, in particular, ruggedized low force switches for applications such as elevator control buttons.
Elevator control buttons are provided in hallways and elevator cars to request and direct elevator service. A particularly popular button utilizes a cold cathode gas tube actuated by the mere touch of the user's finger. The tube also glows to provide illumination indicating a service request. Its activation results from the capacitance associated with the user's finger when touching a control terminal on the button connected to the gas tube. It is quite understandable that a particularly appealing feature of this button is the "soft touch" imparted to the user simply because no mechanical motion or force is required for its activation. Furthermore, because no force is required, the temptation to pound repeatedly on the button is minimized significantly. The application of the cold gas tube in an elevator control button is the subject of the following U.S. patents, wherein its operation is described in much amplified detail: U.S. Pat. Nos. 2,525,767; 2,525,768 and 2,525,769.
In certain other elevator installations, mechanical type switches are used in lieu of the gas tube. Needless to say, it is still preferred and desired to achieve the "soft touch". In fact, some of these installations are retrofits for the gas tube button and use the switch apparatus described in commonly owned, copending application Ser. No. 952,223, TRANSISTORIZED ELEVATOR CONTROL BUTTON, filed Oct. 17, 1978 by Brooks.
An exceptionally appealing way to achieve this end is to use low force switches, particularly those characterized by nearly imperceptible movement for actuation and more importantly a very low force requirement, usually about 1.5 grams; for example, as shown in U.S. Pat. No. 3,862,381 to Glaister, et al. A particularly attractive switch of this type contains a small dot of conductive material mounted on a flexible cover. A light force is applied to the cover, in the area of the dot, in order to press its dot against a grid of conductive material connected to the switch terminals. The dot shorts the grid to complete the circuit between the terminals. The flexible cover is usually thin and has inherent resiliency which causes the switch to recover to its normal nonactuated condition when the force is removed therefrom. Suffice it to say, these switches are particularly fragile and delicate; sharp blows or excessive or concentrated force on the cover can result in damage thereto, not to mention the dot and the grid. The result can be a dramatic reduction in useful switch life.
An elevator control button, needless to say, is particularly vulnerable to harsh and abusive treatment from its various, sundry users. Practical considerations dictate that an elevator control button must contain a touch or pressure plate of reasonably large surface area so as to enable a user to conveniently touch it. Generally speaking, a useful area will be considerably larger than the area on the cover of these low force switches to which force is applied for actuation; see, for example, U.S. Pat. No. 4,033,030 to Robinson, et al. The force applied to the pressure plate therefore must be concentrated into a small area for actuation, and hence, there is considerable possibility that the switch will be damaged by a user who applies too much pressure, sustained pressure or pounds repeatedly on the button. For this reason, the use of commercially available low force switches of this type, as well as other related types, in elevator control buttons has been heretofore impractical; principally because the switch would have an undesirably short service life.